Cycloaddition of Ketene Acetals with 4-Bromo-6-spiroepoxycyclohexa-2,4-dienone.

4-Bromo-6-spiroepoxycyclohexa-2,4-dienone reacts as a diene in an inverse electron-demand reaction with 1-ethoxy-3-methoxy-1-trimethylsilyloxybuta-1,3-diene but as a dienophile with 1-ethoxy-3-methylene-4-(ethoxy trimethylsilyloxymethylene)-1-cyclohexene.